It's an extra decoupled stage in the high voltage line. It provides more filtering to the preamp.  I believe it's part of the original circuit. The filtering is a good thing in a higher gain amplifier. No need to jump it.

How do the two amps compare in sound??

Just finished working on a 2204.
TIP: you want to knock the hum down a bunch?
Move the ground wire on the Preamp filter cap (The cap marked A, B) from the star ground to the middle of the ground buss.